Urbanization Pressures Alter Tree Rhizosphere Microbiomes

Soil microbial community (SMC) provides critical ecosystem services. Plants, specifically trees, act as soil ecosystem engineers controlling SMC structure/composition. Tree species in temperate and boreal forests are considered keystone species as well as ecosystem engineers strongly influencing nutrient resources within the soil environment driving differences in SMC. Additionally, tree location within a complex and changing landscape can result in SMC composition that is more immediately susceptible to the influence of anthropogenic inputs. Finally, urban forest trees offer the ideal experimental system to evaluate whether natural (i.e., plant) or anthropogenic (i.e., altered environment) factors have the greatest effect on SMC structure and distribution. Knowledge of potential controls governing the ecosystem structure (e.g., community patterns) and function (e.g., nutrient pools) of urban soils is of critical importance as the transformation of natural and agricultural land towards urban and suburban settlement continues to expand. The objectives of this study were: i) determine if tree species influence has a greater control over bacterial community composition than forest edge effects (e.g., edge vs. interior) and/or urbanization pressure., ii) identify bacterial groups driving community composition differences (i.e., similarity vs. dissimilarity) corresponding to tree location and forest type, and iii) categorize urbanization pressures as determined via soil chemistry observations (i.e., pH, organic matter, heavy metals and C/N) in order to identify factors altering rhizosphere bacterial community structure of urban soils.